Journal of Maps

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Geomorphological evolution of the plain between the Livenza and Piave Rivers in the sixteenth and seventeenth centuries inferred by historical maps analysis (Mainland of Venice, Northeastern Italy)

Paola Furlanetto & Aldino Bondesan

To cite this article: Paola Furlanetto & Aldino Bondesan (2015) Geomorphological evolution of the plain between the Livenza and Piave Rivers in the sixteenth and seventeenth centuries inferred by historical maps analysis (Mainland of Venice, Northeastern Italy), Journal of Maps, 11:2, 261-266, DOI: 10.1080/17445647.2014.947341 To link to this article: https://doi.org/10.1080/17445647.2014.947341

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Geomorphological evolution of the plain between the Livenza and Piave Rivers in the sixteenth and seventeenth centuries inferred by historical maps analysis (Mainland of Venice, Northeastern Italy) ∗ Paola Furlanettoa and Aldino Bondesanb aAkeo, Padova, Italy (private company); bDepartment of Geosciences, University of Padova, Padova, Italy (Received 2 September 2013; resubmitted 14 July 2014; accepted 18 July 2014)

The ancient hydrographical network and geomorphological framework of the fluvial and coastal plain encompassed between the Livenza and Piave Rivers in the mainland of Venice (Northeastern Italy) were reconstructed, based on historical maps, georeferenced, and overlaid on available geomorphological maps and aerial photographs. A selection of 59 maps was accurately analyzed (32 from the sixteenth century, 31 from the seventeenth century, and 6 from the eighteenth century). They were selected by author, commitment, date, and scale, from among more than 1000 maps edited by Savi e Esecutori alle Acque (the ‘hydrographical’ service during the Republic of Venice) in the 16th and seventeenth century. The most representatives (7 from the sixteenth century and 6 from the seventeenth century) were georeferenced and redrawn. Finally, four 1:50.000 maps were created, picturing the ancient morphology and hydrographical network in the years 1550, 1600, 1650, and 1700, covering an area of about 130 square kilometers. Geographical information was compared with historical documents and geological, geomorphological, and geochronological data. Further comparison of geodetic maps from the eighteenth to the twenty-first century produced new maps with important information on the paleogeographical and environmental framework across two centuries, and particularly on the artificial diversion projects performed by the Venetian Republic, their effectiveness, and the geomorphological changes both related to human intervention and recent climatic changes. Keywords: Historical cartography; Lagoon of Venice; alluvial geomorphology; Friuli- Venetian plain; fluvial diversions; Piave River; Livenza River

1. Introduction The ancient hydrographical network and the geomorphological framework of the fluvial and coastal plain between the Livenza and Piave Rivers, located on the northeastern side of the Vene- tian lagoon (Northeastern Italy), has been reconstructed. The present lagoon constitutes a remnant of the old belt of lagoons that used to rim the northern Adriatic coast until the completion of land reclamation projects, which were started in the Renaissance (sixteenth century) and concluded in the period from the end of the nineteenth century to the second half of the twentieth.

∗Corresponding author. Email: [email protected]

# 2014 Aldino Bondesan 262 P. Furlanetto and A. Bondesan

The mainland of the Venetian lagoon underwent a complex geomorphological transformation triggered by continuous fluvial diversions carried out by the Republic of Venice, mainly during the sixteenth and seventeenth centuries, to drive the main fluvial outlets outside of the lagoon. The oldest maps, dating to the first decades of the sixteenth century, portray a lagoon that is very different from the present setting. The surface area was smaller (about 1/3 of the present surface area) because of subsidence and marine transgressions (Dorigo, 1983; Canal, Cavazzoni, 2004). The marked prevalence of fresh water or brackish water contributed to the rapid burial of large lagoon areas. The change to a more continental environment seems to have been triggered by marine regression enhancing fluvial sedimentation in the lagoon. Progressive sedimentary infilling of the lagoon is attributed by Venetians to fluvial deposition causing a reduction in water-surface area and canal closure. Tidal inlets narrowed and become shallower due to littoral transport of fluvial sands from the deltas belonging to the main rivers discharging into the sea close to the lagoon (Adige, Brenta, and Bacchiglione Rivers, to the south and the Piave River to the north). The result was a state of economic and environmental crisis. As a result the Republic of Venice began a huge program of artificial rivers diversions, lasting almost two centuries and causing changes to both the channels and mouths of the Po, Brenta, Bacchiglione, Marzenego, Sile, Piave, Livenza, and minor rivers. After work on the Bacchiglione, Brenta, and Marzenego (1507–1530), Venice began to divert the course of the Piave River out of the lagoon area on the left side of the river, to both prevent sand from being transported (thereby creating sandbars and shallow water) and to avert floods from affecting Torcello and Murano, causing serious damage to the lagoon. The four maps of the Livenza-Piave plain area (see Main Map) show, from the oldest carto- graphic representation of 1550 to the end of 1600, how the fluvial and coastal system changed during the two centuries when the greatest interventions took place. At the end of the transformations, not only had the hydraulic network changed radically but also the sedimentary dynamics and geomorphological setting of the entire alluvial plain, lagoon, and coastal stretch.

2. Methods The four maps presented herein are part of a wider research project called the Imago (Image Map Archive GIS-Oriented) Project. This project is primarily devoted to the implementation of a data- base concerning 350 historical maps of the Lagoon of Venice and its fringe (Bondesan & Furlanetto, 2012; Fozzati et al., 2012; Furlanetto & Primon, 2004; Furlanetto, Bondesan, Levor- ato, Rosselli, & Bertani, 2009; Furlanetto, Bondesan, Rosselli, Pacquola & Rasador, 2004; Meneghel & Bondesan, 2004; Fontana et al., 2010; Fontana et al., 2014; Francese et al., 2014). The ancient hydrographical and geomorphological context has been reconstructed using historical maps that were georeferenced and overlaid on available geomorphological maps and aerial photographs. The final goal was the diachronic reconstruction of the hydrographic and geo- morphologic changes in the Lagoon of Venice and its hinterland during the sixteenth and seven- teenth centuries: the four presented maps show a part of the study area, in particular, the territory between Livenza and Piave. The project, which began in 2001 and ended in 2011, was funded by Magistrato alle Acque-Consorzio Venezia Nuova – Informative Service of Venice, through a pro- tocol with the National Archives of Venice. The latter has collected more than 100,000 historical maps and related documents, which were issued as fundamental documents for the decree of acts by the Republic of Venice from the fifteenth to the eighteenth century, to exert administrative control over the territory. Esri ArcGis 9.3 was used to georeference all of the studied maps to the same coordinate system (ED1950, Gauss-Boaga projection) and integrate different supporting geodatabases. The main data Journal of Maps 263 came from: (1) geomorphological map (1:20,000; Bondesan & Meneghel, 2004; Bondesan et al., 2004); (2) geological map (1:20,000; Bondesan, Primon, Bassan, & Vitturi, 2008); (3) soil map (1:50,000; Giandon et al., 2001) and (4) a map of the archaeological landscape (1:50,000; Furla- netto, 2012). A comparison was performed through the overlay analysis with topographic maps from the seventeenth to the twenty-first century: the most geometrically accurate being the Topo- graphisch-geometrische Kriegs karte von dem Herzogthums Venedig made by Anton Von Zach in 1797–1805 (Rossi, 2005); the topographic survey of Auguste De´naix (1809–1811); the map of Antonio de Bernardi made in 1843; the Topographic Map of the Lombardo Veneto Reign drawn by the Austrian Imperial Royal General Staff made in 1833 (Austrian General Staff, 1833); and the historical National Topographic Map series (1:25,000 scale) printed by the Geographical Mili- tary Institute since 1861. We also made use of aerial photographs, mainly 1:17,000 to 1:33,000 scale, taken since 1943 and available at the Cartographical Office of the region of Veneto. The thir- teen most-representative historic maps were georeferenced, and the major landforms and geo- graphical information redrawn; through these analyses, four maps at a scale of 1:50,000 were created, depicting historic morphology and hydrology in 1550, 1600, 1650, and 1700. For the georeferenced maps, the root-mean- square error (RMSE) for each control point was reviewed. Where this error was greater than 200 m (more common for lagoon areas due to a lack of a sufficient number of control points) and where the automatic distribution of the errors resulted in poor overlay, we split the map in to smaller sections. These were georeferenced and sub- sequently mosaicked. Once all of the maps were georeferenced, each element was rechecked, repositioned, and adapted through a comparison with elements present on the geomorphological map and in the preceding, contemporary and later topographic maps. For a correct understanding of the maps, we consulted available literature and cartographic sources relating to them, such as detailed titles and a legend printed along the map border and explanatory notes that were attached to the maps, as well as manuscripts often compiled by the same cartographers. A special protocol was then adopted to assign a ‘reliability score’ to each map, considering a weighted value for each map attribute, such as author, depicted area, scale, density of topographic features, number of geo- graphic control points, etc. The geographical and geomorphological information contained on the historic maps were redrawn using a geographical information system, through which 27 different layers were extracted. The main features are: water courses (in the lagoon and in the mainland), fluvial ridges, lakes, lagoons, beach dunes, roads, islands, fisheries, lagoon canals, salt marshes, tidal flats, reeds, swamps, woods, grazing, embankments, coastal defenses, and the coastline. Original toponyms and hydronyms were added to the synoptic maps. The oldest maps, from the fifteenth and sixteenth centuries, were originally drawn not accord- ing to a geographical projection, but just using large-distance-visible topographic points. In the past, the astrolabe made use of fixed points, such as towers and churches, from which a windrose was traced, setting the direction and distance of single elements. We georeferenced the historic maps using the Technical Regional Map (1:5000) as a basemap; the main problem was finding a sufficient number of common GCPs (Ground Control Points). The river courses are the main elements considered for georeferencing because many canals and rivers change in time, and the traces of palaeochannels inferred from photointerpretation were very useful for finding more GCPs. We considered only confluence points or artificial patterns that were clearly matched in the historic maps, excluding meanders or sinuous rivers that could have changed over time. A polynomial transformation was used to correct the maps spatially. GCPs were spread out over the entire raster dataset in order to achieve the best first-order results; second- or third-order transformations were also performed. The RMSE was generally under 200 m, dependent on the scale of the map. Resampling the raster dataset was performed using the nearest neighbor algorithm. 264 P. Furlanetto and A. Bondesan

3. Geomorphological setting The low plain between Piave and Livenza belongs to the distal part of the Nervesa megafan formed during the Last Glacial Maximum (LGM) from Piave sediments (Carton et al., 2009). The alluvial plain, formed from the LGM to the Holocene, hosts a characteristic alternation of overbank, crevasse, natural levee, and floodplain deposits with common thin peat intercalations (Amorosi, Fontana, Antonioli, Primon, & Bondesan, 2008; Bondesan & Meneghel, 2004; Bondesan et al., 2008; Fontana, Mozzi, & Bondesan, 2008; Fontana, Mozzi, & Bondesan, 2010; Miola et al., 2006). In addition, peat formation occurred in poorly drained depressions where organic production prevailed over alluvial minerogenic sediment delivery, both during the LGM and historic time (Baroni, Zanchetta, Fallick, & Longinelli, 2006; Bondesan, Calderoni, & Rizzetto, 2003; Miola et al., 2006). This part of the Venetian mainland was extensively occupied by lagoons, marshes, and swamps, crossed by canals that often discharge into the Adriatic Sea. Starting from sixteenth century, many projects were carried out for land reclamation and deviation of the main rivers, pre- venting the fluvial sediments from entering the lagoon and depositing sands along the littoral and across the lagoon inlets (Bondesan & Furlanetto, 2004). This long and complex series of natural avulsions in historical time and human interventions since the thirteenth century led to the excavation of swampy canals, to the opening of lagoons inlets, the construction of fluvial embankments, and the cutting of rivers. Venetian engineers oper- ated to stop the rivers discharging into the northern lagoon, diverting them into the old Piave riv- erbed (the present Piave Vecchia), in order to drive sediment discharge outside the lagoon; they altered the Zero, Dese, Marzenego, Sile, Vallio, and Meolo Rivers. The Sile, Piave, and Livenza Rivers were part of a huge complex of hydraulic works, with the excavations of new large riverbeds and canals. Then, a great lake (‘Lago della Piave’) was estab- lished to receive the water and sediments of the Piave, which are largely responsible for the coastal sedimentation in front of Venice. Then, in 1683, following bank collapse at Landrona, the Piave River flowed spontaneously toward Cortellazzo, similar to its present course, reflecting local, favorable geomorphologic context and corresponding to the main paleo-Piave River.

4. Conclusions Historical maps serve as a powerful tool for geomorphological analysis and paleohydrographic reconstruction, in particular in areas affected by rapid morphologic change and modified by human activity. Use of the historic maps of Venice has been particularly effective because of the extraordinary number of available maps. They were considered important for territorial management by the senate of the Republic, which is also the reason why an important cartographic school developed in Venice, particularly during the sixteenth and seventeenth centuries. The maps likely illustrate the largest and longest series of artificial fluvial diversions in a single territory within Italy. Historic maps are usually considered reliable starting from the eight- eenth century, when maps were drawn according to geographical projections, but even the most ‘pictorial’ maps dating to the fifteenth century can be georeferenced if compared with elements that we can recognize in modern topographical and geomorphological maps. The study area has shown a great complexity of fluvial diversions and hydrographic interventions that caused an extensive territorial change. This transformation has been monitored through the last five cen- turies, thanks to the historic maps, which helped in reconstructing the cause-effect morphogenetic processes. Journal of Maps 265

Software Esri ArcGIS 9.3 was used for map production.

Data The list of historical maps used to draw the four maps are listed in Table 1. The supplementary file contains information about each map as they were archived into the Data Base Imago.

Acknowledgments The authors would like to thank the reviewers Maria Cristina Salvatore, Francesco Ferrarese, Bastiaan Note- baert, and Heike Apps for their valuable comments on the manuscript. This research is part of the Imago Project funded by Magistrato alle Acque-Consorzio Venezia Nuova and MIUR (Italian Ministry for Edu- cation, University and Research) funds (Bondesan). The authors acknowledge Silvia Pacquola and Agnese Rasador for the data base compiling and map production.

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